We intend to compare transport of a variety of organic and inorganic nutrients at the anterior and posterior faces of the bovine lens. The classes of substances to be studied include amino acids, sugars, phosphate, purines, pyrimidines and their nucleoside and nucleoside phosphates. The ocular lens offers and unusual opportunity to study differentiation in an intact tissue, as the epithelial cells line the anterior surface, and portions of the fiber cells, which have been formed from epithelium, are present at the posterior surface. (The entire structure is covered by a collagenous capsule). Uptake of amino acids at a number of systems of transport (A-, L-, Ly ion-, ASC-sites, etc.) is to be examined. We also hope to continue to classify the system(s) of transport which exist for the nucleosides and related compounds. Kinetic studies will be done to obtain quantitative information on these systems, and to define the specificity of the transporters in the plasma membranes. The effect of aging on transport in the bovine lens is to be evaluated. Data on influx and efflux will be expressed on the basis of unit area (anterior or posterior surface). Transport in the rat lens will be compared with that in the bovine lens as qualitative differences have been found in systems for amino acids, and the smaller, more active rodent lens has advantages when metabolizable substrates are investigated.